Method and apparatus for removably coupling a blowout preventer stack to an underwater wellhead casing

ABSTRACT

Use of an elongated, tapered and apertured guide tool extending beneath a blowout preventer stack for sealable insertion into an existing underwater wellhead casing to control final descent and placement of the blowout preventer stack collet connector in coupling position relative to the wellhead casing.

United States Patent Inventor Durward B. Jones Houston, Tex.

Appl. No. 796,357

Filed Feb. 4, 1969 Patented Sept. 7, 1971 Assignee Offshore Systems Inc.

Houston, Tex.

METHOD AND APPARATUS FOR REMOVABLY COUPLING A BLOWOUT PREVENTER STACK TO AN UNDERWATER WELLHEAD CASING 16 Claims, 2 Drawing Figs.

US. Cl 166/.5, 166/75 lnt.Cl ..E2lb 33/035 Field of Search 166/.5, .6; 175/5, 7

[56] References Cited! UNITED STATES PATENTS 3,177,703 4/1965 Waters et al 1. 166/16 X 3,330,339 7/1967 Johnson 166/.6 3,313,347 4/1967 Crain i. 166/.5 3,461,958 9/1969 Brown 1 166/.5 3,474,858 10/1969 Gibson et al 166/.5

Primary ExaminerJames A. Leppink Assistant ExaminerRichard E. Favreau Attorneys-John A. Crowley, Jr. and Alvin H. Fritschler ABSTRACT: Use of an elongated, tapered and apertured guide tool extending beneath a blowout preventer stack for scalable insertion into an existing underwater wellhead casing to control final descent and placement of the blowout preventer stack collet connector in coupling position relative to the wellhead casing.

PATENTEDSEP nan 11603385 DURWARD BURROUGHS JONES FIG. I0 68 I WMWZWW ATTORNEYS METHOD AND APPARATUS FOR REMOVABLY COUPLING A BLOWOUT PREVENTER STACK TO AN UNDERWATER WELLHEAD CASING The drilling and completion of offshore oil and gas wells involves a series of complicated operations initiated from a floating vessel, which take place in the vicinity of the sea floor normally hundreds of feet therebeneath. This if further complicated by the fact that even in calm seas, the floating vessel 1 coupled to the conductor pipe just below the housing. The

guide base is supported by a rather large diameter base template in the form of a hollow cell, filled with cement and having a central opening for receiving the downwardly extending conductor pipe.

With the conductor pipe and permanent guide base in position, guide posts and guide lines extend upwardly therefrom to the surface for guiding subsequently lowered equipment. Generally, the guide lines which extend upwardly from the guide post are attached to some portion of the drilling rig carried by the floating vessel and appropriate means are employed for maintaining constant tension on the guide line when running equipment. Snatch blocks are employed, and due to wave action or water currents, the guide lines tend to feed off except during running of the equipment.

The conductor housing supports the exposed wellhead casing which constitutes an upwardly extending cylindrical member, internally of the guide post or frame. The wellhead casing effectively supports in nested fashion, multiple tubes of decreasing diameter which in turn receive the rotating drill pipe during active drilling. conventionally, control equipment, such as the blowout preventer stack is subsequently lowered onto and coupled to upper end of the wellhead casing while being guided by the guide posts and cables. Any intense fluid pressure occurring within the drilled hole, tends to eject the drilling string, etc. at high speed causing destruction to the guide base and any attending equipment.

When the well extends more than several hundred feet beneath the sea floor, it is usual to install blowout preventers in multiple stacked form. A blowout preventer stack is guided into position on the guide base, and coupled by a suitable collet connector or other device to the upwardly extending open wellhead casing. in the past, since a typical blowout preventer stack weighs in excess of l00 tons, the lowering of this as sembly onto the guide base, even through the employment of the upwardly extending guide lines and guide posts, results in frequent damage to the lower collet connector or female coupling member carried by the blowout stack preventer or to the rather fragile cylindrical wellhead casing. This is partially due to the fact that the equipment is lowered from a surface vehicle which is constantly pitching even in light seas. Further, the rise and fall of several feet tends to slam the collet connector into contact with the wellhead even though they both may be in axial alignment. This is true, even where a telescopic joint is coupled between the drill pipe extending downwardly from the floating vessel and the upper end of the blowout preventer stack, for counteracting the effect of the pitching surface vessel.

The connection between the lower end of the blowout preventer stack and the cylindrical wellhead casing is achieved through the employment of a female collet connector or its equivalent which normally forms the lowermost element of the blowout preventer stack. it has an internal diameter compatible with the external diameter of the wellhead casing. Attempts have been made to employ sensing means for sensing the relative position between the descending blowout preventer stack and the wellhead casing or guide base so that the rate of descent of the blowout preventer stack may be abruptly decreased as the collet connector nears the wellhead casing to prevent destruction ofeither member.

The problem of pitch of the surface-oriented lowering ap paratus, has, to such an extent, affected the rate of final descent of the collet connector and the accurate determination of the instantaneous location of these two elements, that frequent partial or total destruction of the wellhead occurs. Once the wellhead casing is damaged, there is no known way for removing and replacing the same, since, the wellhead casing is relatively massive, and normally supports a series of strings of tubing with the tubing as well as the wellhead casing and conductor pipe being rigidly set in cement and fixed to each other,

Once the actual connection is achieved between the lower female collet connector and the wellhead casing, it is necessary to test the fluid seal between these elements. In this respect, the pivotable collet segments carry sealing means which either operate alone, or in cooperation with sealing means carried by the exposed wellhead casing. In the past, after positioning the blowout preventer stack and coupling the lower collet connector to the wellhead casing, the special tool employed during connection was removed by raising the marine riser to the surface whereupon, another specially formed tool was lowered into contact position with the wellhead casing. The open end of the wellhead casing normally flares outward and this special tool included a tapered tip and an O-ring carried thereby for achieving a high'pressure fluid seal between the testing tool and the flared wellhead casing. Fluid under high pressure is then delivered to the space existing between the specially formed tool, the interior of the lower collet connector and, in fact, a portion of the vertical casing forming a part of the blowout preventer stack and surrounding the vertically extending specially formed testing tool. if a proper sealed connection exists between the lower collet connector and the wellhead casing, this is is readily indicated by the maintenance of the high pressure of the captured fluid. However, if an improper and unsealed connection occurs between the lower collet connector and the wellhead casing and fluid pressure is lost, it is necessary to remove the blowout preventer stack and check the lower collet connector for damage while running a similar check for damage on the fixed wellhead casing. In any case, assuming a proper sealed connection exists, it is nor mally necessary to remove the special testing tool with the tapered tip and O-ring prior to initiating redrilling of the well. The cost of the prior testing technique may involve sums as high as $2,000 or more covering time required in removing the running tool subsequent to collet connection, placement of the special tapered tool carrying the O-ring, pressurizing the blowout preventer stack and sensing the maintenance or loss of fluid pressure due to a correct or incorrect sealed connectorjoint.

It is therefore, a primary object of this invention to provide an improved method and apparatus for removably coupling a blowout preventer stack to an underwater wellhead casing which prevents destruction to either the lower collet connector or the wellhead casing, regardless of the amount of pitch of the surface vessel.

It is a further object of this invention to provide an improved method and apparatus for coupling a blowout preventer stack to an underwater wellhead casing wherein the position of the descending blowout preventer stack in proximity to the fixed wellhead casing is made immediately and accurately known to the operator on the surface vehicle.

It is a further object of this invention to provide an im proved method and apparatus for removably coupling a blowout preventer stack to an underwater wellhead casing wherein the lower collet connect is accurately guided onto the upstanding wellhead casing at a closely controlled rate of descent correlated to the mass of the blowout preventer stack.

It is a further object of this invention to provide an improved method and apparatus for removably and coupling a blowout preventer stack to an underwater wellhead casing whereby testing of the collet connection for high-pressure fluid sealing may be readily and immediately achieved after connection of the lower collet connector to the wellhead casing without requiring the use of a special testing tool.

Further objects of the invention will be pointed out in the following detailed description and claims and illustrated in the accompanying drawings which discloses, by way of example, the principle of the invention and the best mode which has been contemplated of applying that principle.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1a is an elevational view, partially in section, of an improved underwater drilling apparatus with a portion with a blowout preventer stack being lowered onto a fixed wellhead casing under the controlled method of the present invention.

FIG. lb is a second portion of the apparatus of FIG. la, partially in section.

In general, the present invention is employed in conjunction with an underwater drilling arrangement employing a drilling template positioned on the sea floor and supporting a guide base, carrying conductor piping with a wellhead casing extending upwardly therefrom. The guide base is provided with a suitable guide frame and posts, which acts to guide a descending blowout preventer stack from a surface vessel lowering the same. A drill pipe and telescopic joint is connected to the blowout preventer stack through an upper collet connector. A lower collet connector on the blowout preventer stack carries a conical, tapered head, seal carrying, hollow running tool which extends downwardly therefrom and which is received by the open wellhead casing. Fluid pressure builds up, behind the seal, in response to insertion of the tapered conical head of the running tool into the wellhead to provide a self-induced fluid pressure brake for slowing the descending blowout preventer stack to a speed which insures against collet connector or wellhead casing damage. The fluid pressure regulates the rate of descent while the tapered conical head accurately locates the lower collet connector relative to the wellhead. Upon seating, the lower collet connector is actuated to achieve a sealed coupling between the blowout preventer stack and the wellhead casing.

Preferably, one various sized replaceable orifice forming member is selectively carried by the hollow, tapered conical head, correlated to the mass of the blowout preventer and the desired descent rate after the pressure seal enters the wellhead casing. Since there is a tendency for momentary reverse movement of the tool due to surface vehiclepitch, multiple pressure seals in cup form are carried by the running too], extending in opposed directions to insure retention of the seal once insertion of the tapered tip of the running tool is achieved.

Upon coupling of the lower collet connector to the wellhead casing, fluid under high pressure is directed into the space between the running tool, the wellhead casing and the coupled collet connector to test the seal between casing, the blowout preventer stack lower collect connector and the wellhead casing, without removing the tapered running tool, since, the cupshaped multiple pressure seals prevent loss of fluid beyond the tapered tip of the running tool.

Referring to the drawings, all of the underwater drilling apparatus is positioned from a surface vehicle 118 which, of course, carries the necessary equipment such as a derrick, etc., for raising and lowering the equipment to and from the sea floor. As shown, and starting with FIG. lb, on sea floor there is provided a drilling template 12 formed of sheet metal or the like, nd once located on the sea floor, it is filled with cement 14 to create massive support member for accurately locating and supporting guide base 16 of conventional construction. A large hole 18 is provided in the drilling template 12 which acts to receive the large diameter conductor pipe 20 carried by the guide base 16 and rigidly welded to the conductor housing 22 at the top of the guide base. Tapered sidewall 24 of the drilling template I2 cooperates with arcuate elements 26 on the lower part of the guide base to provide a balland socket-type connection between the guide base 16 and the drilling template 12, thus facilitating subsequent connection between the lowered equipment and the equipment already present on the sea floor.

As mentioned previously, a wellhead casing 28 is disposed on the conductor housing in conventional fashion, such that the conductor housing supports the smaller diameter conductor pipe 30 as well as any subsequently inserted drill string casings. Cement in conventional fashion is employed as a seal between the concentric pipes as well as to unify the structure. Should the specially formed upper end 30 of the wellhead casing be damaged, the usefulness of the complete assembly ceases and it is necessary to move to another location and redrill the well. Thus, the guide base and all of the elements carried thereby are lost while the equipment is moved to a new location and drilling commences again. In this respect, it is noted that the wellhead casing 28 is provided with an annularly recess 32 downwardly of its open end with the open end 30 tapering outwardly to provide a frustoconical inner surface 34 which acts as a guide for subsequently inserted casing or drill pipe.

Further, as evidenced in FIG. lb, the blowout preventer stack 36 carries at its lower en, a collet connector 38 which essentially comprises a large diameter cylindrical housing 40 carrying a plurality of individual, circumferentially arranged, segmental collet elements 42 which may be cammed outwardly under impact of surfaces 44 against the ends 30 of the wellhead during stock descent. This allows the collet segments to ride over the same whereupon surfaces 44 fall into the annular recess 32 formed on the wellhead. The lower collet connector 38 is conventional, and includes fluid pressure motors (not shown) for camming the collets in a counterclockwise direction about pivot point 46 to securely lock, in sealed fashion, the blowout preventer stack onto the wellhead casing once the collet connector has been appropriately positioned over the same. Proper positioning during descent of the massive blowout preventer stack 36 is achieved by the multiple guide posts 48 which are fixably coupled to opposed sides of the guide base 16. In this respect, it is normal to use four guide posts, although only two are visible in the present elevational view. The guide posts 48 extend upwardly and as shown in FIGS. 1a and 1b, are received within hollow cylindrical guide frame members 50, which are carried by and form a part of the blowout preventer stack 36. The cylindrical guide frames taper outwardly at 52 at their bottoms, to ensure proper reception of the upstanding guide post 48 as the massive blowout preventer stack is lowered on the guide lines or cables 54, one for each guide frame cylinder 50.

The preventer stack 36 therefore constitutes an open frame arrangement, rectangular in configuration and in all other respects is conventional. Specifically, the stack comprises four ram-type preventers indicated at 5 6, 58, 60 and 62, respectively and a single bag type preventer 64 of the hydri1" type. Each ram-type preventer extends transversely of the well axis, and as indicated in FIG. la, preventer 60, in partial section, shows opposed pipe rams 66 positioned relative to the running tool 68 with their inner ends received within lateral recesses 70 on opposed sides of the running tool. In conventional fashion, the rams may act as a blind rim and multiple drill pipe rams for the various sized drill pipe employed during the drilling operation. This is subsequent to placement of the blowout preventer stack 36 in position with the lower collet connector 38 locked to the upper end of the wellhead 28. The preventers employ hydraulically operated ram locking means (not shown) to achieve, as a result of remote control initiation, locking of the pipe rams in the position, as with preventer unit 60. The occurrence of extreme pressures within the well which could initiate a destructive blowout of the well tubing, etc. Of course, during the lowering and actual connection of the blowout preventer stack 36 to the wellhead casing, one of the rams, such as 68, are extended in their position as additional means to rigidly lock the running tool 60 onto the descending preventer stack 36.

As mentioned previously, the blowout preventer stack employs collet connector 38 to physically couple, in sealed fashion, the blowout preventer stack to the wellhead casing. The collet connector is also hydraulically operated and may include a mechanical override to ensure positive locking upon reaching coupling position relative to the guide base and wellhead casing. Appropriate gasket means (not shown) are car ried by the collet segments 42 which cooperate with the outwardly tapered tip 30 of the wellhead to insure a high-pressure fluid seal between these elements once coupling is completed. Appropriate fluid pressure lines and coupling means '72 and '74 function either to feed high-pressure fluid to the connectors 40 operating the same in a selective manner, and as means to sense and remove accumulated well-casing fluid under emergency conditions. During the last few feet of descent of the blowout preventer stack on the apertured running tool, and proper location of the lowered collet connector relative to the wellhead, well-casing fluid moves under high pressure upward through the drill pipe in a manner to be described in detail hereinafter.

The bag-type preventer 64 or hydril, comprises a flexible annulus which, under applied high fluid pressure moves in wardly against the surface of the drill pipe or running tool, passing therethrough, to frictionally grab the drill pipe in a full circumferential manner and to thereby prevent further upward movement under the relatively high fluid pressure developed within the well bore. The bag-type preventer 6 1 provides a frictional grip, sufficient to overcome hydraulic pressures operating on the drill pipe on the order of 3,000 pounds per square inch.

Immediately above the bag-type preventer 6%, there is located an upper collet connector 70 which normally forms a part of the marine riser 00. The function of the marine riser is to return the drilling fluid to the surface vehicle and to furnish access to the well for the drill pipes, etc. being run. A ball and socket joint may be provided at the lower end of the drill pipe 07., although as shown in FIG. 111, there is provided a drill pipe to running tool crossover 8 1. Connecting clamp means d6 couple the crossover to the upper collet connector 70. Fixed to the crossover 0 1, is the upper end of running tool 68, the tool passing through the center of the hydril 6 1, and the four ram-type blowout preventers 56, 5%, 60 and 62 as well as the lower collet connector 30. As mentioned previously, in addition to employing the ram-type blowout preventer to prevent the high-pressure ejection of elements from the well insofar as the present invention is concerned, one of the ram type preventers such as preventer 60, acts as a positive coupling means for the specially formed running tool 60 to assist the running tool crossover 1341 in maintaining the same in its desired axial position on the blowout preventer stack.

The drill pipe 02 carries therewith, a telescopic joint 83 in the form of concentric casing members 1141 and 116, the telescopic joint connection being also conventional and necessary since, the floating vessel is constantly rising and falling due to the surface action. The marine riser 00 in the present application is run with the blowout preventer stack 36 and forms a material element thereof. Suitable clamps such as till are employed for coupling in an axially stacked manner, the various elements such as hydril 6 1, the blowout preventers and the lower collet connector 38.

A principal element of the apparatus of the present invention comprises the running tool 68 which is formed of a nonflexible metal of rod-shaped form carrying a small diameter bore or hole 90 through the center thereof. The running tool 68 is counterbored and threaded at 92, at its lower end, and has coupled thereto a tapered, conical head 9 1 which is also provided with a control bore or hole 96 of like diameter to bore 90 of the running tool. The tip of the head 96 is provided with a replaceable orifice forming, cylindrical plug 93, each plug having a different diameter bore, with this bore being correlated to the mass of the blowout preventer stack 36.

Further, the running tool is provided with a pair of oppositely directed pressure seals formed of rubber or plastic material, cup shaped in configuration, and sandwiched between the end of the running tool 60 and a recessed portion 101 of the tapered conical head 9d. The lower cup-shaped seal 100 opens up in a downward direction while the upper cup-shaped seal 102 is oppositely oriented. In this respect, the outer diameter of the pressure seal, prior to insertion within bore 10 1 of the wellhead, is of a diameter slightly in excess thereto whereby, an extremely good hydraulic seal is completed between the inserted running tool tapered conical head 9 1, and the wellhead casing 20.

The configuration of the running tool, especially the employment of the cup-shaped seals 100 and 102 effectively pro vides another important aspect of the present invention. In addition to properly aligning the descending collet with respect to the stationary wellhead, and upon achieving a seal between the running tool and the wellhead casing, braking the descending blowout preventer stack, the present apparatus allows the immediate determination of whether or not a proper fluid seal exists between the lower collet connector and the wellhead casing to which it is coupled. In this respect, by forcing highpressure fluid through the pipe 745 and coupling 108, fluid enters between the hollow vertical casing 77 and the running tool and fills the gap between the running tool, the lower collet connector 38 and that portion of the space between the running tool and the wellhead casing bore 104 rearwardly of the cup-shaped seals 100 and 1102. Upon pressurizing this space, if any fluid is lost, it will be due to an unsealed connection between the lower connector 38 and the wellhead casing 23. That is, connection may be achieved without a proper seal between these members. This is in contrast to the prior art testing method, which required specially formed testing tool having a tapered end carrying a sealing member which would effectively form a seal between the inserted tool and the flared, tapered entry surface 34 of the wellhead casing. in the instant system, there is no necessity for removing the running tool facilitating the initial connection between the lower collet connector and the wellhead casing and reinserting a special testing tool, since the placement of the cup-shaped seal facilitates the retention of a high-pressure seal between the running tool and the lower collet connector.

in operation, the running tool 68 is coupled to the blowout preventer stack by means of the running tool crossover 841. Upper collet connector 7% functions to connect to the drill pipe 02 and the telescopic joint 83 to the upper end of the preventer blowout stack 36. The one of more of the individual blowout preventer assemblies 56, 58., 60 or 62 may be further employed to fixedly locate the intermediate portions of the running tool 68 relative to the blowout preventer stack during descent.

Assuming that the guide base 16 and wellhead 28 are in position on the base template beneath the sea, the blowout preventer stack is lowered on guide lines 541 and the guide posts 40 at relatively high speed, in spite of the fact that the blowout preventer stack assembly may be in excess of 100 tons. As the blowout preventer stack nears the guide base and wellhead casing, the hollow cylindrical guide frame elements ride over the upstanding guide posts 43, the tapered conical head 94 of the running tool moves into the open end of the wellhead casing 2d guided by the corresponding tapered surfaces 34% of the wellhead casing, and. surfaces 104i of the conical head. The accumulated fluid within the well hole and the wellhead casing, is displaced by the descending tapered conical head SM. At the instant that the cup-shaped pressure seals 100 and 102 enter the wellhead bore 104, a seal is completed relative to wellhead casing bore 104, and the captured fluid cannot escape around the outside of the running tool, but must pass upwardly through the tapered conical head bore 96, the central running tool bore and the drill pipe. The captured fluid within the well acts as a self-operating hydraulic brake for the descending massive blowout preventer stack. The final rate of descent is closely controlled by correlating the size of the replaceable orifice forming plug 98 with the overall mass of the blowout preventer stack. Normally, the diameter of the orifice is less than the diameter of either bore 96 in the conical head or bore 90 of the running tool, such that the orifice acts as the controlling element. Obviously, not only is the lower collet connector, therefore, properly located with respect to the wellhead casing and centered therewith, but, due to the fluid resistance, the blowout preventer stack moves the last few feet or inches at a predetermined limited speed, which is slow enough to prevent damage to either the wellhead casing or the lowered collet connector 38. Means generally referred to by the numeral 120 may be coupled to the hollow running tool for sensing the increase in pressure of the fluid within the wellhead casing after insertion of the running tool, as an indication of the relative position between the descending blowout preventer stack and the fixed guide base. Note further, that the configuration of the oppositely oriented pressure seal not only provides pressure sealing in two directions, but also ensures proper operation of the system components regardless of slight tilting or misalignment between the axis of the wellhead and the descending running tool and blowout preventer stack. Once the lower collet connector is properly seated, as defined by abutment face 110 of the fixed element 112 of the lower collet connector and the edge 30 of the wellhead, hydraulic means are employed to pivot the lower collet connector segments 42 about their pivot point 46 to seal and lock the lower collet connector to the wellhead casing.

The locking of the lower collet connect to the wellhead casing should provide a fluid seal between these elements which may be tested by forcing high pressure into the space therebetween. This fluid is prevented from passing downwardly through bore 104 of the wellhead casing 28 by the presence of the cup-shaped seals and, therefore, should there be a failure to provide a fluid seal between the lower collet connector segment and the wellhead casing, the loss of fluid pressure would indicate the same.

Subsequent to proper positioning and connecting of the blowout preventer stack relative on the guide base and wellhead casing the blowout prevcnters 56, 58, 60 and/or 62 may be moved to inoperative position and the drill pipe and upper collet disconnected and returned to the surface, carrying therewith, the specially formed running tool 68 which is employed only for properly orienting and controlling the rate of the massive blowout preventer stack during its final few feet of descent onto the guide base.

While this invention has been described in conjunction with the coupling of the blowout preventer stack to an established wellhead, it is understood that the same sequence may be employed with a similar or identical running tool for facilitating either mud line suspension, or marine completion subsequent to drilling.

While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that the foregoing and other changes in the form and details may be made therein without the parting from the spirit and scope of the invention.

What is claimed is:

1. A method for lowering a guided blowout preventer stack onto an underwater guide base having guide members extending to the surface for coupling said stack to an unsealed cylindrical wellhead casing extending above said guide base comprising:

a. placing said preventer stack on said guide members in alignment with said wellhead casing, said preventer stack having a vertically positioned running tool with a small bore extending therethrough in fluid communication with the surface, said running tool projecting downward below said blowout preventer stack in axial alignment with said wellhead casing;

b. lowering said preventer stack so that said running tool engages and passes downward within said wellhead casing; and

c. effecting a seal between'the outer surface of said vertically positioned running tool and the inner surface of the wellhead casing preventing the flow of fluid from said wellhead casing to the surrounding sea, the thus-captured fluid in the wellhead casing acting as a brake for the descending blowout preventer stack, the controlled rate of flow of said fluid upward through said bore in the vertically disposed running tool controlling the rate of descent of said blowout preventer stack onto the underwater guide base in position for coupling to said wellbore casing, whereby the rate of descent of the massive blowout preventer stack may be carefully controlled so as to minimize any possibility of damage to the wellhead casing and to the lower end of the preventer stack due to slamming of the lower end of said stack into the wellbore casing because of too rapid descent of said stack or the pitching of the surface vessel from which said stack is lowered.

2. The method of claim 1 in which the rate of fluid flow upward in the bore in said vertically disposed running tool is controlled by an orifice positioned in said bore.

3. The method of claim 1 in which the lower end of the blowout preventer stack comprises a lower collet connector adapted for coupling to said unsealed wellhead casing and comprising sealably coupling the collet connector to the cylindrical wellbore and thereafter, without removing said vertically disposed running tool, forcing fluid into the space between said vertically disposed tool, the inner surface of said lower collet connector and that portion of the space between said tool and the wellhead casing bore rearwardly of the means for effecting a seal between said vertically disposed tool and the inner surface of said wellhead casing, any loss of fluid forced into said space indicating an unsealed connection between the lower collet connector and the wellhead casing.

4. The process of claim 1 and including measuring the pressure of the fluid in said wellhead casing, the increase in pressure upon efiecting said sealing contact between the vertically positioned running tool and the wellhead casing being an indication of the relative position of the descending blowout preventer stack and the underwater guide base.

5. An apparatus for controlling the rate of descent of a blowout preventer stack on guide posts and guide wires extending to the surface in axial alignment with an unsealed cylindrical wellhead casing extending above an underwater guide base comprising:

a. a vertically positioned running tool extending through and projecting downward below said blowout preventer stack in axial alignment with the wellhead casing, said running tool having a small bore extending therethrough in fluid communication with the surface, said vertically positioned tool having an outside diameter less than the inside diameter of said wellbore casing; and

b. sealing means secured to the outer surface of said vertically positioned running tool at a point on the lower portion of said vertically positioned tool below said blowout preventer stack, said sealing means being adapted to provide sealing contact with the inner surface of said wellbore casing, so as to prevent the flow of fluid from said wellbore casing to the surrounding sea, the thus-captured fluid in the wellhead casing acting as a brake for the descending blowout preventer stack, the controlled rate of flow of said fluid upward through the bore in the vertically disposed running tool controlling the rate of descent of said blowout preventer stack onto the underwater guide base in position for coupling to said wellbore casing, whereby the rate of descent of the massive blowout preventer stack may be carefully controlled so as to minimize any possibility of damage to the wellbore casing and the lower end of the blowout preventer stack due to slamming of the lower end of said stack into the wellbore casing because of too rapid descent of said stack or the pitching of the surface vessel from which said stack is lowered.

6. The apparatus of claim and including fluid pressure sensing means in communication with fluid passing upwardly through said vertically positioned running tool for sensing the increase in pressure of the fluid within said wellhead casing after insertion of said vertically positioned tool therein and the establishment of sealing contact between said tool and the inner surface of said wellhead casing, said increase in pressure serving as an indication of the relative position between the descending blowout preventer stack and the underwater guide base.

7. The apparatus of claim 5 in which said sealing means comprises radially extending sealing member positioned on the exterior surface of said vertically positioned running tool, said members being adapted to make sealing contact with the bore of said wellhead casing upon insertion of said vertically positioned running tool therein as the blowout preventer stack is lowered from the surface to the underwater guide base.

8. The apparatus of claim 7 in which said radially extending sealing members comprise at least one cup-shaped seal carried by said vertically positioned running tool.

9. The apparatus of claim 5 and including orifice defining means carried by said bore containing, vertically positioned running tool, said orifice controlling the rate of flow of fluid from said wellhead casing upward in the bore of said vertically positioned tool.

10. The apparatus of claim 9 in which the diameter of said orifice is less than the diameter of said bore in the vertically positioned tool.

11. The apparatus of claim 5 and including a conical head section secured to the lower end of said vertically positioned tool, said conical head tapering inward at the lower portion thereof to facilitate insertion thereof in said wellhead casing, said conical head section having a bore extending vertically therethrough in fluid communication with the bore in said vertically positioned tool, said sealing means comprising radially extending sealing members positioned on the exterior surface of said vertically positioned tool at the lower portion thereof, said members being adapted to make sealing contact with the bore of said wellhead casing upon insertion of said vertically positioned running tool therein as the blowout preventer stack is lowered from the surface to the underwater guide base.

12. The apparatus of claim 111 and including a replaceable orifice-forming plug positioned at the tip of said conical head section to regulate the rate offluid flow from the wellhead casing upward through said head section and said vertically positioned running tool.

13. The apparatus of claim 11 in which said sealing members comprise at least a pair of cup-shaped pressure seals carried by said vertically positioned tool behind said tapered conical head section, said seals being oppositely oriented to insure an effective seal between said vertically positioned tool and said wellhead casing regardless of momentary reversal in direction of movement of the blowout preventer stack during its descent.

14. The apparatus of claim 11 in which the lower end of said blowout preventer stack comprises a collet connector for coupling to the wellhead casing and including: (a) sealing means carried by the collet connector for causing a fluid seal between said collet connector and said wellhead casing during coupling thereof, and (b) means for directing fluid under high pressure to the space between said collet connector, the wellhead casing and the vertically positioned running tool rearwardly of said sealing means to test the adequacy of the fluid seal between the coupled collet connector and the wellhead casing.

15. The apparatus of claim 14 and including orifice-defining means carried by said bore-containing, vertically positioned running tool, said orifice regulating the rate of fluid flow from said wellhead casing upward in the bore of said vertically positioned tool.

116. The apparatus of claim 15 in which said orifice means comprises an orifice-forming plug positioned at the tip of a conical head section, said head section being secured to the lower end of said vertically positioned running tool, said conical head tapering inward at the lower portion thereof to facilitate insertion thereof in said wellhead casing, said conical head section having a bore in said vertically therethrough in fluid communication with the bore in said vertically positioned running tool, the diameter of said orifice being less than the diameter of the bore in said conical head section and said vertically positioned running tool. 

1. A method for lowering a guided blowout preventer stack onto an underwater guide base having guide members extending to the surface for coupling said stack to an unsealed cylindrical wellhead casing extending above said guide base comprising: a. placing said preventer stack on said guide members in alignment with said wellhead casing, said preventer stack having a vertically positioned running tool with a small bore extending therethrough in fluid communication with the surface, said running tool projecting downward below said blowout preventer stack in axial alignment with said wellhead casing; b. lowering said preventer stack so that said running tool engages and passes downward within said wellhead casing; and c. effecting a seal between the outer surface of said vertically positioned running tool and the inner surface of the wellhead casing preventing the flow of fluid from said wellhead casing to the surrounding sea, the thus-captured fluid in the wellhead casing acting as a brake for the descending blowout preventer stack, the controlled rate of flow of said fluid upward through said bore in the vertically disposed running tool controlling the rate of descent of said blowout preventer stack onto the underwater guide base in position for coupling to said wellbore casing, whereby the rate of descent of the massive blowout preventer stack may be carefully controlled so as to minimize any possibility of damage to the wellhead casing and to the lower end of the preventer stack due to slamming of the lower end of said stack into the wellbore casing because of too rapid descent of said stack or the pitching of the surface vessel from which said stack is lowered.
 2. The method of claim 1 in which the rate of fluid flow upward in the bore in said vertically disposed running tool is controlled by an orifice positioned in said bore.
 3. The method of claim 1 in which the lower end of the blowout preventer stack comprises a lower collet connector adapted for coupling to said unsealed wellhead casing and comprising sealably coupling the collet connector to the cylindrical wellbore and thereafter, without removing said vertically disposed runNing tool, forcing fluid into the space between said vertically disposed tool, the inner surface of said lower collet connector and that portion of the space between said tool and the wellhead casing bore rearwardly of the means for effecting a seal between said vertically disposed tool and the inner surface of said wellhead casing, any loss of fluid forced into said space indicating an unsealed connection between the lower collet connector and the wellhead casing.
 4. The process of claim 1 and including measuring the pressure of the fluid in said wellhead casing, the increase in pressure upon effecting said sealing contact between the vertically positioned running tool and the wellhead casing being an indication of the relative position of the descending blowout preventer stack and the underwater guide base.
 5. An apparatus for controlling the rate of descent of a blowout preventer stack on guide posts and guide wires extending to the surface in axial alignment with an unsealed cylindrical wellhead casing extending above an underwater guide base comprising: a. a vertically positioned running tool extending through and projecting downward below said blowout preventer stack in axial alignment with the wellhead casing, said running tool having a small bore extending therethrough in fluid communication with the surface, said vertically positioned tool having an outside diameter less than the inside diameter of said wellbore casing; and b. sealing means secured to the outer surface of said vertically positioned running tool at a point on the lower portion of said vertically positioned tool below said blowout preventer stack, said sealing means being adapted to provide sealing contact with the inner surface of said wellbore casing, so as to prevent the flow of fluid from said wellbore casing to the surrounding sea, the thus-captured fluid in the wellhead casing acting as a brake for the descending blowout preventer stack, the controlled rate of flow of said fluid upward through the bore in the vertically disposed running tool controlling the rate of descent of said blowout preventer stack onto the underwater guide base in position for coupling to said wellbore casing, whereby the rate of descent of the massive blowout preventer stack may be carefully controlled so as to minimize any possibility of damage to the wellbore casing and the lower end of the blowout preventer stack due to slamming of the lower end of said stack into the wellbore casing because of too rapid descent of said stack or the pitching of the surface vessel from which said stack is lowered.
 6. The apparatus of claim 5 and including fluid pressure sensing means in communication with fluid passing upwardly through said vertically positioned running tool for sensing the increase in pressure of the fluid within said wellhead casing after insertion of said vertically positioned tool therein and the establishment of sealing contact between said tool and the inner surface of said wellhead casing, said increase in pressure serving as an indication of the relative position between the descending blowout preventer stack and the underwater guide base.
 7. The apparatus of claim 5 in which said sealing means comprises radially extending sealing member positioned on the exterior surface of said vertically positioned running tool, said members being adapted to make sealing contact with the bore of said wellhead casing upon insertion of said vertically positioned running tool therein as the blowout preventer stack is lowered from the surface to the underwater guide base.
 8. The apparatus of claim 7 in which said radially extending sealing members comprise at least one cup-shaped seal carried by said vertically positioned running tool.
 9. The apparatus of claim 5 and including orifice defining means carried by said bore containing, vertically positioned running tool, said orifice controlling the rate of flow of fluid from said wellhead casing upward in the bore of said vertically positioned tool.
 10. The apparatUs of claim 9 in which the diameter of said orifice is less than the diameter of said bore in the vertically positioned tool.
 11. The apparatus of claim 5 and including a conical head section secured to the lower end of said vertically positioned tool, said conical head tapering inward at the lower portion thereof to facilitate insertion thereof in said wellhead casing, said conical head section having a bore extending vertically therethrough in fluid communication with the bore in said vertically positioned tool, said sealing means comprising radially extending sealing members positioned on the exterior surface of said vertically positioned tool at the lower portion thereof, said members being adapted to make sealing contact with the bore of said wellhead casing upon insertion of said vertically positioned running tool therein as the blowout preventer stack is lowered from the surface to the underwater guide base.
 12. The apparatus of claim 11 and including a replaceable orifice-forming plug positioned at the tip of said conical head section to regulate the rate of fluid flow from the wellhead casing upward through said head section and said vertically positioned running tool.
 13. The apparatus of claim 11 in which said sealing members comprise at least a pair of cup-shaped pressure seals carried by said vertically positioned tool behind said tapered conical head section, said seals being oppositely oriented to insure an effective seal between said vertically positioned tool and said wellhead casing regardless of momentary reversal in direction of movement of the blowout preventer stack during its descent.
 14. The apparatus of claim 11 in which the lower end of said blowout preventer stack comprises a collet connector for coupling to the wellhead casing and including: (a) sealing means carried by the collet connector for causing a fluid seal between said collet connector and said wellhead casing during coupling thereof, and (b) means for directing fluid under high pressure to the space between said collet connector, the wellhead casing and the vertically positioned running tool rearwardly of said sealing means to test the adequacy of the fluid seal between the coupled collet connector and the wellhead casing.
 15. The apparatus of claim 14 and including orifice-defining means carried by said bore-containing, vertically positioned running tool, said orifice regulating the rate of fluid flow from said wellhead casing upward in the bore of said vertically positioned tool.
 16. The apparatus of claim 15 in which said orifice means comprises an orifice-forming plug positioned at the tip of a conical head section, said head section being secured to the lower end of said vertically positioned running tool, said conical head tapering inward at the lower portion thereof to facilitate insertion thereof in said wellhead casing, said conical head section having a bore in said vertically therethrough in fluid communication with the bore in said vertically positioned running tool, the diameter of said orifice being less than the diameter of the bore in said conical head section and said vertically positioned running tool. 